Orthopedic procedures for the replacement of all, or a portion of, a patient's joint have been developed over the last thirty years. Currently, the procedures used to prepare the bone and seat the implants are generally referred to as open procedures. For the purposes of this discussion, the term “open procedure” will refer to a procedure wherein an incision is made through the skin and underlying tissue to fully expose a large portion of the particular joint surface. In both total and unicondylar knee arthroplasty, the typical incision for an open procedure can be about 7-12 inches long. After the initial incision in the skin, the internal wound can be enlarged to fully expose the areas to be prepared. While this approach provides surgeons with an excellent view of the bone surface, the underlying damage to the soft tissue, including the muscles, can lengthen a patient's rehabilitation time after surgery. While the implants may be well fixed at the time of surgery, it may be several weeks or perhaps months before the tissues violated during surgery are fully healed.
Unicompartmental knee arthroplasty can be utilized to correct a varus or a valgus deformity caused by, e.g., osteoarthritis affecting the medial (a varus deformity) or lateral (a valgus deformity) compartment of the knee. Traditionally, unicondylar knee arthroplasty is an open procedure in which a surgeon, after exposing the knee, resects diseased or otherwise undesirable bone from the appropriate compartment of the knee, including portions of the distal femur and the proximal tibia. The distal femur and proximal tibia of the affected compartment are also shaped to receive a unicondylar knee prosthesis.
In traditional unicondylar knee arthroplasty, leg alignment requires a trial and error technique in which the surgeon makes a distal femoral cut and a proximal tibial cut and thereafter selects the location of the other of the distal femoral cut and the proximal tibial cut based on experience and the knowledge that tibial prostheses are available in a limited number of thicknesses. Typically, the proximal tibial cut is made so as to remove the least amount of the proximal tibia, while ensuring sufficient removal of diseased or otherwise undesirable bone. The remaining femoral cuts can be made to complete shaping of the femur to receive a femoral prosthesis. After the femoral and tibial cuts are complete, the femoral prosthesis and the tibial prosthesis, or provisional versions thereof, can be temporarily implanted and leg alignment reviewed by the surgeon. If the tibial prosthesis does not include an integral bearing component, then a discrete bearing component can also be implanted. To adjust alignment of the leg, the surgeon can replace the tibial prosthesis or bearing component with an alternative tibial prosthesis or bearing component having an increased or decreased thickness. The surgeon can also recut the femur to achieve appropriate alignment. Additionally or alternatively, the surgeon can remove more tibial bone stock and again insert the previously used tibial prosthesis, or replace the previously used tibial prosthesis with a tibial prosthesis of a different thickness. This procedure of trial and error can be conducted until the surgeon believes that the appropriate alignment has been achieved.